The impact of model resolution on the simulated Holocene retreat of the Southwestern Greenland Ice Sheet using the Ice Sheet System Model (ISSM)

Abstract

Abstract. Geologic archives constraining the variability of the Greenland Ice Sheet (GrIS) during the Holocene provide targets for ice sheet models to test sensitivities to variations in past climate and model formulation. Even as data-model comparisons are becoming more common, many models simulating the behaviour of the GrIS during the past rely on meshes with coarse horizontal resolution (≥ 10 km). In this study, we explore the impact of model resolution on the simulated nature of retreat across Southwestern Greenland during the Holocene. Four simulations are performed using the Ice Sheet System Model (ISSM); three which use a uniform mesh and horizontal mesh resolutions of 20 km, 10 km, and 5 km and one non-uniform mesh with resolution ranging from 2 km to 15 km. We find that the simulated retreat can vary significantly between models with different horizontal resolutions based on how well the bed topography is resolved. In areas of low topographic relief, model resolution plays a negligible role in simulated differences in retreat, with models instead responding similarly to surface mass balance (SMB) driven retreat. Conversely, in areas where the bed topography is complex and high in relief, such as fjords, lower resolution models (10 km and 20 km) simulate unrealistic retreat driven as ice-surface lowering intersects bumps in the bed topography which would otherwise be resolved as troughs in the higher resolution models. Our results highlight the important role that high resolution grids play in simulating retreat in areas of complex bed topography, but also suggest that models using non-uniform grids can save computational resources through coarsening the mesh in areas of non-complex bed topography where the SMB drives retreat. Additionally, these results emphasize that care must be taken with ice sheet models when tuning model parameters to match reconstructed margins, particularly for lower resolution models in regions where complex bed topography is poorly resolved.

Ocean‐Driven and Topography‐Controlled Nonlinear Glacier Retreat During the Holocene: Southwestern Ross Sea, Antarctica

“…Nonlinear deglaciation of the southwestern Ross Sea then occurred—defined here as the episodic retreat (Greenwood et al., 2018; Lee et al., 2017) and abrupt increase in the thinning rate (Jones et al., 2015, Jones et al., 2020) of outlet glaciers—despite this region currently accommodating some of the coldest waters in Antarctica (Orsi & Wiederwohl, 2009; Smith et al., 2012). The spatial and temporal pattern of deglaciation has been difficult to replicate in ice sheet models, possibly because the model resolutions used are too coarse to accurately represent the complex bed topography in this region (Cuzzone et al., 2019; Lowry et al., 2019). Key questions therefore remain regarding the drivers and controls of recorded nonlinear ice‐sheet behavior in the southwestern Ross Sea during the Holocene.…”

Insolation vs. meltwater control of productivity and sea surface conditions off SW Greenland during the Holocene

“…Once off the shelf, GrIS retreat across the mainland seems to have occurred rapidly from c. 11.4 to 10.4 ka BP in the Nuuk region (Larsen et al 2014(Larsen et al , 2017. High summer insolation and temperatures during the Early and Middle Holocene lasted until about 5 ka BP (Briner et al 2016) and resulted in a simulated GrIS ice mass loss rate of about 100 Gt a -1 (Lecavalier et al 2014;Larsen et alf 2015;Cuzzone et al 2019). The Late Holocene experienced a cooling related to reduced summer insolation that presumably favoured the growth of the GrIS, ice caps and local glaciers since about 4000 years ago (Funder et al 2011;Briner et al 2016;Larsen et al 2017;Schweinsberg et al 2018).…”

The Utrecht Finite Volume Ice-Sheet Model: UFEMISM (version 1.0)

“…4 require input files describing the present-day Antarctic ice sheet and climate. For the ice-sheet and bedrock geometry, we used the Bedmachine Antarctica v1 data by Morlighem et al (2019) which is freely available as supplementary material to their publication. For the present-day climate we used the ERA-40 reanalysis (Uppala et al, 2005), which can be downloaded from the ECMWF website (https://www.ecmwf.int/) after creating a free user account.…”

“…CC BY 4.0 License. (Cuzzone et al, 2018(Cuzzone et al, , 2019, they tend to be too computationally demanding for the 10 5 -10 7 yr simulations needed for paleoice-sheet simulations.…”